In the late 1940s the quadrilateral socket was introduced to the United States, and during the intervening years since its introduction the "quad socket" has been the standard design for fitting a prosthetic limb to the residual thigh of an above-knee amputee. During the approximately 40 years in which the quad socket has been employed in the United States it has become clear, however, that there are certain problems, particularly as to comfort and stability, inherent to the use of the quad socket.
Although there are many variations to the quad socket, it consistently presents a horizontally oriented brim at the proximal posterior. The horizontal brim serves as the ischial seat upon which the user's ischial tuberosity is supported. In fact, that portion of the user's weight which would normally have been supported by the amputated limb is transferred to the quad socket through the ischial seat.
The geometry of the quad socket purposely provides a rather narrow dimension, measured from the anterior to the posterior wall of the socket, in relation to the medial/lateral dimension. The aforesaid dimensional relationship of the quad socket was selected to assure that the socket applies pressure on the anterior of the residual thigh to push the ischium toward the posterior of the socket in order that the ischial tuberosity will be forced to rest solidly on the ischial seat presented by the brim at the proximal posterior of the socket. To accommodate the compression of the thigh which results within the quad socket because of the purposely narrowed anterior/posterior dimension, the medial/lateral dimension of the socket is made relatively larger.
However, the enlarged medial/lateral dimension makes it virtually impossible to provide sufficient lateral support for the distal end of the femur in the residual limb, as would be required to eliminate a limp during that portion of the user's gait when the artificial limb is in the weight bearing mode and the sound leg is swinging through to the next step. In fact, many knowledgeable commentators are of the opinion that the quad socket is ineffective in all but the mid-stance phase of the gait due to the excessive abduction of the femur permitted within the quad socket because of the aforesaid dimensional relationship.
Recognition of the deficiencies inherent to the quad socket is, in effect, a challenge to the basic concept that the ischial tuberosity should serve to transmit the majority of the weight expected to be carried by the residual limb to the ischial seat provided for that purpose on the quad socket. Such a challenge recognizes that the structural arrangement of the quad socket has the basic inability to stabilize the femur when the gluteus medius fires; the arrangement of the quad socket, after all, provides no structure whereby the ischium is able to preclude abduction of the femur. It is this inability to stabilize the femur which results in the necessity for the user to lean laterally in an attempt to stabilize the pelvis, thus presenting the readily recognizable limp required of a person using the quad socket.
Specifically, as the gluteus medius pulls the femur into abduction, the pelvis slides medially because the ischial tuberosity is free to shift along the ischial seat of the quad socket; The unsupported femur has little choice but to abduct in a more pronounced attitude within the wide medial/lateral dimension of the quad socket. The pronounced abduction imposes pain at the distal end of the femur as well as at the proximal medial portion thereof. To reduce the undesirable pressure, and the resulting pain, the patient leans to position the torso over the abducted, distal end of the femur.
The aforesaid negative characteristics of the quad socket can be obviated by a much more recent innovation in prosthetic sockets which employs a narrower medial/lateral dimension and a wider anterior/posterior dimension, the relative dimensions being chosen such that the ischial tuberosity and a portion of the ramus of the ischium is contained within the socket. The recently developed, narrow medial/lateral socket configuration also employs a relatively high lateral wall which provides medially directed reactive forces proximal and distal to the greater trochanter. In this arrangement the abduction angle of the femur in the residual limb more closely approaches that of the femur in the sound extremity during all portions of the user's gait, thus greatly reducing the characteristic limp.
This recently developed socket design is not, however, designated by a universally accepted appellation. At present such a socket design is designated as a "N.S.N.A. (Normal Shape Normal Alignment) socket," or a "narrow ML (Medial/Lateral) socket" or a "Cat-Cam (Contoured, Adducted Trochanteric, Controlled, Aligned Method) socket." The most recent improvement of an ischial containment socket which has the desired, relatively narrow, medial/lateral dimension is disclosed and claimed in my copending U.S. patent application, Ser. No. 099,778, filed on Sept. 22, 1987. Irrespective of the name employed, in order to provide an effective socket which incorporates the narrow medial/lateral dimension a more precise fitting of the socket to each patient is normally required for the narrow medial/lateral socket, as are multiple tests of the socket prior to fabrication of the finished prosthetic limb. Nevertheless, the greater comfort and the improved functionality that can be achieved by this new design has been thought to offset the inconvenience, and increased cost, at least to those who can afford both the time and expense.
Except when using the prefabricated interface unit disclosed in the aforesaid U.S. patent application, Ser. No. 099,778, to fabricate either the historic quad socket or the more recently developed, narrow medial/lateral socket, the prosthetist employs a negative model of the amputee's residual thigh. To assure comfort to the user, it is necessary that the negative model comfortably contain the residual limb and reflect the position assumed by the residual limb when it is bearing the amputee's weight. The load bearing disposition of the residual limb constitutes the condition when the residual limb and the prosthesis are subjected to the most stress and are most likely to cause discomfort to the amputee. Therefore, the prosthetist attempts to fabricate the interface portion of the socket such that it will provide the maximum support during the weight bearing mode.
Heretofore negative castings of the residual limb in its weight bearing disposition have been made by casting a plaster mold of the thigh while the amputee is standing with his limb in a casting brim. A casting brim incorporates a number of individual pads which can be separately adjusted to engage the residual limb in a manner which attempts to mimic a prosthetic socket and thereby provide maximum support to the residual limb of the individual patient.
Once the several pads of the casting brim are disposed in what the prosthetist deems to be the most appropriate arrangement to mimic a prosthetic socket for the individual patient, the patient then removes his limb from the brim. A plaster casting material is interposed between the casting brim and the residual limb in such a way that it fully encapsulates the residual limb. When the casting material has hardened it comprises a negative model of the residual thigh in the weight bearing position, and that negative model is used in the production of a positive reproduction of the residual limb to which the interface portion of the prosthetic socket is fitted.
In order to assure comfort to the patient, and to accommodate the bio-mechanics occasioned by the interaction between the residual limb and the prosthetic socket, the primary, technical objective of the interface is to maintain the femur of the residual limb in an attitude comparable to the disposition of the femur in the sound leg. This can become quite complicated as the prosthetist seeks to fabricate a comfortable interface, and particularly when using many of the brim casting techniques employed in fitting quadrilateral sockets.
A brief description of one of the more successful brim casting techniques for fitting the narrow, medial/lateral socket (which technique has a satisfactorily easy learning curve for the prosthetist and provides consistently positive results for the patient) will immediately substantiate the considerable improvement which results from the use of an interface fitting module embodying the concepts of the present invention. The typical brim casting technique requires several accurate measurements. First, the circumference of the residual limb is measured at approximately two inch 5.08 cm increments along the length of the residual limb. The length of the residual limb, measured from the ischial tuberosity, must be known, and three unique medial/lateral measurements, and a rather different anterior/posterior measurement, must be precisely taken. The medial/lateral measurements are taken, as follows:
1. A firm medial/lateral measurement must be taken one or two inches distal to the ischium. This measurement is referred to as the Distal Ischial Tuberosity measurement--i.e., the DIT--and is taken with large caliper pads so as not to over compress the flesh of the residual limb in a medial/lateral direction.
2. A first medial/lateral measurement must be taken from the medial side of the ramus of the tuberosity to a point just superior to the greater trochanter of the femur. This measurement is referred to as the Oblique medial/lateral dimension--i.e., the OB--and is a bony measurement which may be taken firmly.
3. A firm medial/lateral measurement is also a bony measurement which may be taken firmly from the medial border of the ramus of the ischium to the subtrochanteric area of the femur. If the ischial tuberosity is palpated, the prosthetist will find that the measurement is actually taken from an area superior and medial to the ischial tuberosity. This measurement is referred to as the ischial tuberosity Medial/Lateral--i.e., the ML.
An anterior/posterior measurement is also taken, but the manner in which the measurement is taken differs from the anterior/posterior measurement taken for fitting quadrilateral socket in that it is a "surface tight," or silhouette, measurement taken with the medial/lateral flesh firmly compressed. With the residual limb compressed in a medial/lateral direction the anterior/posterior dimension is slightly elongated, and it is the elongated anterior/posterior dimension which is measured. Finally, the femoral adduction angle is measured with the patient holding the limbs as though the knees were pressed together into tight adduction with the pelvis.
The pads of the brim are then selectively positioned in a brim stand in conformity with the aforesaid measurements. In brief, the procedure entails:
1. Levelling the pad which constitutes the posterior wall of the brim.
2. Orienting the medial and lateral pads of the brim such that they are disposed at a declining angle (on the order of 10.degree. to 20.degree.) from the lateral to the medial wall. This is necessary for the ischial tuberosity to be contained within the socket and for the public ramus to remain out of the socket.
3. Setting the adduction angle on the lateral bar of the brim into conformity with that angle, as measured on the patient.
4. Setting the DIT as measured from the patient, plus approximately 1/4 inch (0.635 cm) to accommodate the thickness of the plaster, on the lateral pad.
5. Checking to be certain that the medial and lateral walls are not parallel but are wider anteriorly in the region of the adductor longus.
6. Positioning the oblique pad so that it will firmly press against the patient proximal to the trochanter with the posterior portion engaging the posterior of the residual thigh at the mid medial/lateral point. The oblique pad should parallel the wing of the ilium.
7. Positioning the anterior pad to the dimension of the patient plus approximately 1/4 inch (0.635 cm), to accommodate the thickness of the plaster.
8. Establishing the circumferential measurement, defined by the brim pad locations, in conformity with the circumferential measurements of the patient's residual limb--plus approximately one inch (2.54 cm) to accomodate the thickness of the plaster.
9. Because this procedure forms a weight bearing cast, the evaluation performed at this step is critical. That is, the procedure continues by palpating the patient's residual limb to assure that: the ischium will be contained within the socket; the public ramus lightly touches the medial wall; the lateral pad firmly contacts the patient; and, the femur is centralized within the flesh of the residual limb. During this evaluation the patient wears a five ply stocking to simulate the plaster wraps subsequently applied to form the negative impression casting.
10. Readjusting the oblique pad snugly to rest against the patient's side.
11. Checking to determine that the ischium is received approximately 1/2 to 3/4 inch (1.270 cm to 1.905 cm) within the socket--too great a depth applies pressure to the coccyx, blocking hip extension. A full range of hip motion is required; adduction or extension must not be blocked.
With the components of the brim thus properly disposed, the brim is prepared by applying, and smoothing, plaster splints to the medial and posterior surfaces of the brim in order to assure accurate copying of the brim contour. The patient is prepared by applying approximately two layers of an elastic plaster wrap over the thin stockinet which shields the patient's residual limb, and thereafter applying approximately two additional layers of a rigid plaster wrap. Preparation of the residual limb is concluded by applying a plaster splint against the proximal trochanteric region which is held firmly in position by the oblique pad. Particular care is taken to provide cover high on the lateral side of the hip, at least to the level of the iliac crest.
After concluding the aforesaid pre-preparation, the patient inserts the covered, residual limb into the brim fixture. The pubis should lightly contact the medial wall of the brim to assure that the residual thigh has been inserted into the brim to the proper depth. The patient then forcefully adducts the residual limb.
If the measurements have been accurately taken, and properly transferred to the brim, the brim will form the proximal socket shape while the prosthetist directs his, or her, attention to the distal aspect of the residual limb. One hand is employed to centralize the femur within the tissue of the residual limb by pulling the distal medial tissue in a lateral direction. The other hand is used to create an angular disposition to the distal, lateral area of the residual limb in order to stabilize the femur and protect the distal end of the residual limb. When the plaster has completely hardened, the brim is lowered and the patient removes the residual limb from the resulting negative casting.
However, even with careful attention to detail while performing the most widely accepted of the prior known interface fitting techniques, it is impossible to assure that a completely satisfactory interface has been fabricated prior to actual use of a socket which incorporates the resulting interface. Thus, it has heretofore been generally required that a plurality of check sockets be made before finalizing the fitting.
Hence, while a plaster cast of the residual limb can provide a highly accurate and effective model for use in fabricating a quad socket, the process often proves time consuming and expensive. Numerous adjustments are often required properly to position the casting brim before the casting can be made. Moreover, the casting process is itself quite involved and requires close attention to detail. Unfortunately, if the casting proves to be improper, the entire process must be repeated.
In addition, the disposition of the residual limb within the casting brim may be such that the limb is unduly flattened against, or too loosely engaging, one of the adjustable brim pads, and the prosthetist can not always determine that situation until the model is completed, or worse, until the patient tries the resulting socket.